Computer generated holograms are known. Considerable developed has occurred related to such holograms. This development can be summarized.
In Use of Fresnel Zone Plates for Materials Processing, Ser. No. 07/612,212 filed Nov. 9, 1990, now Ser. No. 07/940,008 filed Sep. 3, 1992, the use of computer generated holograms to patterning is set forth. In the preferred embodiment, a plate containing a plurality of holograms is disclosed. Such holograms are confined to subapertures and scanned by coherent light to produce from the subapertures as they are scanned the desired working images for processing materials.
In a Continuation-In-Part Patent Application to be filed Jan. 3, 1994, improved techniques of dimensioning and fabricating the subaperture, creating amplitude modulation with the phase plate, and finally controlling amplitude with optical features beyond the limit of prior art producible optical elements are disclosed. The apparatus for the process, the process and the plate for utilization in the process are set forth.
This application is addressed to how subapertures on plates should be dimensioned and placed side-by-side for efficient scanning and broadcast of their respective images. In a first portion of this application, a technique for dimensioning and placing subapertures in contiguous side-by-side relation is set forth. In a second portion of the application, the problem of taking a subaperture and obtaining from the subaperture a desired real working image profile is set forth. The preferred embodiment incudes combining both of these techniques to secure a small, compact plate configuration which can be efficiently scanned to produce a desired array of working images.
A very broad class of applications of computer generated holograms (CGH) is to reshaping the intensity pattern of a coherent source in one plane (CGH plane usually contained in a transmissive plate) so that it takes on some specified form on another surface. Examples of this are materials patterning (disclosed in the above referenced patent applications) and optical interconnects (set forth in "Optical Interconnections for VLSI Computational Systems using Computer Generated Holography", M. Feldman, Ph.D. thesis, University of California at San Diego, 1989).
In general, we have found that the best techniques to creating arbitrarily complex patterns of working images utilizes subaperture broadcast CGH. Then the problem of generating the entire pattern efficiently subdivides itself into the more numerous but more tractable problem of placing the subapertures efficiently and thereafter producing each feature from its respective subaperture.
At this juncture, the substance of the referred to patent applications can be generalized.
In a patterning application, to produce an array of circular vias or working images of different sizes, the actual shape and configuration of the working images or vias is assumed at a working distance from a plate on to which the subaperture CGHs are to be formed. Once the shapes and their working distances are known, the phase and amplitude modulation required on the plate are determined by backpropagation, Gerchberg Saxton, or some other technique.
An example of this is shown in FIGS. 1-3. These figures illustrate backpropagation as applied to making a feature. Referring to FIG. 1, imaginary point source P1 is located behind the workpiece surface 3, on which feature (here along line 1, 2) is to be made. FIG. 2 shows the amplitude profile (A) defining the feature between points 1, 2. In addition to amplitude modulation, the feature can also subject the outgoing wave to phase modulation. Exemplary phase modulation is illustrated by FIG. 3.
It has previously been emphasized that there is generally a need to laterally displace a subaperture generating a working image. This need arises from design flexibility. If the point source, P1, can be shifted to position P1' this has the effect of changing the subaperture size and location from line 4-5 to line 6-7. The change in subaperture size results in a change in gain.
In the backpropagation technique, a spherical wave emanating from a point, line or plane source is incident from behind the feature and its wavefront is modulated by the features on the mask; especially the wave's amplitude is modulated in accordance with the feature shape. In addition to the amplitude, we can also modulate the outgoing phase. As will hereafter be set forth, it is the modulation of that outgoing phase to which a portion of the following disclosure is directed.